Powertrain, generic (extended)

P2ACE Reductant Temperature Sensor B Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P2ACE means the signal of reductant temperature sensor B lies below its valid voltage band. With the NTC elements used for DEF temperature, a low voltage translates into an extremely hot reading, so a signal line rubbing through to ground, a crushed connector or DEF that has wicked into the plug and bridges the contacts are the usual suspects. No maker publishes a threshold for P2ACE. For sensor A, Deutz lists P2044-00 as a short to ground; GM's 2025 DEF controller sets the low limit of its tank sensor at 0.3 V, roughly 75 °C, which shows the order of magnitude. A false hot value can lead the controller to skip DEF heating in frost, so lines may freeze and dosing stop. Measure the sensor resistance against a temperature table and look for crystallised DEF at the connector.

Likely causes

Signal wire of sensor B shorted to ground
DEF wicked into the connector bridging the terminals
Sensor B internally shorted

Symptoms

  • Check engine light and SCR warning
  • Implausibly high DEF temperature in live data
  • Frozen DEF lines in winter

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–900
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

reductant temperature sensor bwiring harness

Related codes

P2ACCP2ACFP2ACDP2AD0P2044

References: serdia.deutz.com, gsi.ext.gm.com, law.cornell.edu.